This invention relates to fluid-cushion supported apparatus, that is to say, to apparatus which, in operation, is supported, at least in part, by a cushion of pressurised fluid formed and contained between the apparatus and a reactive surface, which may be land or water. One example of gas-cushion apparatus comprises a gas-cushion supported vehicle.
The fluid cushion may be contained, at least in part, by an inflatable flexible skirt system.
Flexible skirt systems comprise two main types, namely segmented or "finger" systems and simple loop or "bag" systems.
The segmented flexible skirt system has been disclosed by British patent specification No. 1,043,351. (U.S. Pat. No. 3.420,330 of Bliss corresponds).
Briefly, this form of flexible skirt system comprises a plurality of contiguous flexible skirt members (or segments) each comprising a sheet of flexible material folded over to provide the member with an outer portion flanked by a pair of side or tie portions, which extend inwardly from the outer portion towards the fluid cushion.
The segmented flexible skirt system is reasonably responsive to variations in reactive surface contour. Thus it is responsive to deflection by waves when used over water. Additionally, the system is reasonably free of shear forces as immediately adjacent flexible skirt members can deflect relative to each other without significant hindrance.
However, segmented flexible skirt systems are prone to wear, due to flagellation at the free bottom ends of the skirt members in the same way as a flag wears out, as well as buckling due to the formation of creases at intermediate points between the upper and lower ends of the skirt members.
The simple loop flexible skirt system has been disclosed by British patent specification No. 1,056,267. (U.S. Pat. No. 3,291,237 of Hopkins et al. corresponds).
Briefly, this system comprises an inflated loop extending between laterally spaced attachment points to present a convex face towards the reactive surface, which face defines a plenum gap with the surface through which fluid surplus to cushion-forming requirements escapes to atmosphere.
The simple loop flexible skirt system tends to have a greater life than that of the segmented system. However, it has substantially less shear freedom, at least in a lateral sense. Furthermore, because it requires large curvatures of loop (imposed by inflation pressure/cushion pressure differentials) in order to maintain system equilibrium and stability, it presents substantial areas of material to the reactive surface whereby frictional resistance is increased.
The present invention provides a fluid-cushion supported apparatus with a flexible skirt system which possesses the advantages of the above-described systems but which can be constructed so as to encounter less frictional resistance than that met by simple loop systems.